The 205 ignition barrel is a simple 4-pole switch. Newer cars have an IGN2 contact which keeps power to the ignition circuit when cranking, so this question does not come up often in other forums. Basically I need power to everything during cranking.
The Jetronic cars deal with cranking by powering up the tachymetric relay via the starter (+D) supply which then holds itself in once RPM is reached.
The Motronic cars seem to have a constant 12V supplied to the ECU, which controls the fuel and injection relays.
I have a PS1000 which draws 330mA @ 12V sitting on a bench. That is high enough to drain the average ~50Ah car battery in a week. So constant 12V is not an option.
You can't just power the ignition from the starter as the ignition will just backfeed a positive. The only thing I can think of is tying the starter motor relay coil positive to the EFI relay coil positive with a diode in between like so. The only failure mode is the starter engaging mid-drive if it short circuits.
I was at the wreckers the other day and noticed some pugs have this brown double relay and going by the diagram it looks like the relays have both the flyback diode and another diode on pin 2 and 14 like so:
Makes me half keen to source one of these relays and connector for my build. I don't have any circuit diagrams to see if those pins are even used in practice. I woulld still be controlling the fuel relay via the ECU.
What have others done? Am I overthinking it?
The Jetronic cars deal with cranking by powering up the tachymetric relay via the starter (+D) supply which then holds itself in once RPM is reached.
The Motronic cars seem to have a constant 12V supplied to the ECU, which controls the fuel and injection relays.
I have a PS1000 which draws 330mA @ 12V sitting on a bench. That is high enough to drain the average ~50Ah car battery in a week. So constant 12V is not an option.
You can't just power the ignition from the starter as the ignition will just backfeed a positive. The only thing I can think of is tying the starter motor relay coil positive to the EFI relay coil positive with a diode in between like so. The only failure mode is the starter engaging mid-drive if it short circuits.
I was at the wreckers the other day and noticed some pugs have this brown double relay and going by the diagram it looks like the relays have both the flyback diode and another diode on pin 2 and 14 like so:
Makes me half keen to source one of these relays and connector for my build. I don't have any circuit diagrams to see if those pins are even used in practice. I woulld still be controlling the fuel relay via the ECU.
What have others done? Am I overthinking it?
